I. Field of the Invention
This invention relates to wireless data transfer systems designed for indoor use. More particularly, the present invention pertains to multipoint-to-point indoor wireless systems and high speed indoor wireless systems utilizing directional antennas to reduce the amount of multipath rays incident to or received by a receiver.
II. Background Art
High speed computer networks using fibers for Gigabit transmissions between network nodes suffer from a series of disadvantages. In some applications, the cost of installing the fiber may be excessive. In addition, the users of such a system may be mobile and therefore need to be untethered. As such, wireless replacements of the fiber links would serve to be a cost-effective and convenient solution.
The design of high speed wireless systems (i.e. data transmission speeds greater than 150 Mb/s) for indoor use, however, requires the consideration of many factors. A major technical consideration is the presence of multipath rays which result from the deflection of a transmitted signal in an indoor environment, e.g. reflections from the floors, walls and furniture in an office or laboratory or the like. The presence of significant multipath rays degrades a system's performance by adding distortion to the transmitted data signal, thereby resulting in an increased bit error rate and slower data transfer.
To achieve the desired high speeds of data transfer, currently employed indoor wireless systems accept the presence of multipath rays and employ multitone or equalization techniques to remove the multipath rays from the data signals after the signals are received by the receiver. An example of such a system is the Motorola Altair System which is capable of transmitting data at a rate of 3.3 Mb/s. Such a system is disclosed in U.S. Pat. No. 5,095,535, herein incorporated by reference. Even though directional antennas are used to remove the multipath in that system, the beamwidth is about 60.degree.. Thus, it is found that significant multipath does remain so that multitone or equalization techniques to achieve an acceptable error rate are necessary. A drawback of this system, however, is that the use of multitone or equalization techniques, which may be implemented by various electronic designs, not only increases the cost of the overall system but, more importantly, slows the rate at which data can be transmitted. Thus, it would be desirable to provide a high speed indoor wireless system having an increased data transfer rate with negligible multipath effects so that multitone or equalization techniques are not required.
A network in which multiple users communicate with a central station is often referred to as a multipoint-to-point system. In a wireless multipoint-to-point system, data is simultaneously received from a variety of remote users transmitting at varying rates in a mix of stream and burst traffic. As such, it would be desirable to provide a multipoint-to-point wireless system in which some form of medium access control is implemented so that the central station can accept and comprehend data transfer, regardless of such factors as the type of traffic involved and the data transfer rates involved.